Wiltproofing paper and method of corrugating



WILTPROOFING PAPER AND METHOD CORRUGATING Herbert N. Johnston and BensonG. Brand, Columbus,

Ohio, and Willis B. Lincoln, Jr., Indianapolis, Ind., assignors, bydirect and mesne assignments, to Inland Container Corporation (Indiana),Indianapolis, Ind., a corporation of Indiana N. Drawing.ApplicationJanuary 27,1955

Serial No 484,582

21 Claims. (Cl. 154 3 3.05)

This invention relates to. the treatment of paper and paperboard sheetsor. webs hereinafter referred to as paper, with a molten, plasticized,resinous composition. The invention is concerned not only with thetreating process and with the treated product, but also with thehereinafter-described treating compositions. 1 A problem of considerableimportance to the paper and paperboard industry is the tendency of thepaper to wilt under conditions of high humidity. The paper tends toabsorb moisture from the air, with the result that the paper fiberssoften and lose their stiffness. Obviously, the ultimate effect is aweakened paperboard structure which will not retain its shapeundernormal handling in transit and storage.

Heretofore, various resinous compositions have been suggested for use inthe molten state to impregnate paper. However, of the known resinouscompositions, none have obtained commercial success because of one ormore of several disadvantages. Substantially thorough impregnation ofthe paper must be obtained 'in order to effectively protect the fibersfrom the absorption of moisture and to effectively stiffen the sheet.The ability of the molten resinous composition to penetrate andimpregmate the paper is related to the viscosity of the composition.Accordingly, the resinuos composition in its molten state must have aviscosity such that it will penetrate and become impregnated or embodiedin the paper. Increasing the temperature of a moltenfresin, of course,decreases its viscosity. However, for paper impregnation pur poses, thetemperature of the molten resin is seriously limited to a low maximumtemperature. H The temperature of the molten resin should not exceedthat temperature at which the paper will char or otherwise becomeheat-damaged. The disadvantage of many of the known moltenresinvimpregnating compositions is that the resin compositions havehigh-melt temperatures and also highmelt viscosities. Thus, in order toobtain substantial wilt-proofing of paper, the molten resin compositionmust have a low-melt temperature and a viscosity at low remperaturewhich will permit rapid. and substantially than ICC ough impregnation orpenetration of the paper by the molten resin composition.

The impregnating material should not form a glossytype coating on thesurface of the paper. In thejjpjroduction of corrugatedpaperboard, solidfibreboard and related products, it is essential that the surface of theimpregnated paper be compatible with a combining adhesive subsequentlyused in the production of manufactured items. That is, the impregnatedpaper should have the fibers exposed so that the paper will accept thead hesive and bind itself to other paper liners.

A further disadvantage of some impregnating agents is that the presenceof the impregnating agents prevents the repulping of the impregnatedpaperfor re-use.

The composition of this invention, comprising fatty acid plasticized,pine wood-type resin, hasbeen fou'ndto give "excellent" wilt-resistantproperties to paperboard and paper. The plasticized resin composition inamolten state is applied to the surface of the paper in the form of acoating, and then heat treated to cause th'epl'asticized resin toimpregnate and penetrate into the paper without the formation of aglossy-type coating. Accordingly, an object of 'this invention is toprovide a wilt-resistant paper. A further object is to provide a'pl'asticizedres'in treated paper, which is characterized by increasedrigidity, even when in contact with an atmo phe're 'o'f high humidity.An additional object of this invention is toobtain' animpregnated paperwhich-does not have 'a' glossy-type coating and which is compatible withcombining or laminating adhesives. A further advantageous feature isthat the impregnated paper of this invention is 'capableof beingrepulped for re-use. As will 'become apparent from the followingdisclosure, an object realized is the'a'pplication of the molten,plasticized resin to the paper at relatively low temperatures, whichwill 'notchar or otherwise heat-damage the paper. It.will be obvious tothose versed in the paper-making and paper-converting arts that theoriginal strength or rigidity of untreated paper will be a determiningfactor, together with other factors, governing rigidity and strengthcharacteristics of the treated sheet of paper.

Other objects and advantages will become apparent from the followingdetailed disclosure and examples. 1

In the following table are set forth examples of various compositions ofthe plasticized resin of the present'inven tion. The paper used inaccordance with these examples is that paper which is used in themanufacture of corrugated fibreboard commonly known as semi-chemicalcorrugating material or medium. Paper made byother well known processessuch as kraft'paper, straw paper,

repulped waste papers, etc., may be used. The percentage values given inthe table are based upon percentage by weight.

3 4; Table Formula Plastletaehleroent composition Test data com ositionEx. Satu- Penetration Concora medium test Per- Per- 7 rated Flow cantcent Oa- Cap- Lau- My- Pal- Ste- Oleic Lin- Linofatty point, resinlasllt. rlo rio rlstic mltlc arlo olelo lenlc acid Per- F. Imme- R. 11.,R. H.,

ticker mix- Sec. cent dlate 50% 85%,

mm 3days 22 75 3 3. 70 179 98. 7 83. 3 38. 7 53 42 3.00 to 4.00 80-85187 99.3 83.7 37.0 54 43 3 3. 00 75 178 108. 7 86. 9 52. 0 54 4.3 3 3.0080 192 99.7 79.8 47.7 54 43 3 3. 00 95 203 108. 7 86. 9 51. 0 54 43 3 3.00 70 186 96. 3 77. 1 50. 7 54 43 3 3.00 60 200 78.3 62.7 41.7 54 43 33.00 40-50 235 7 90.7 72.6 31.3 92 6 2 3. 43 90 170 89. 3 81. 7 35. 3 6036 4 3.62 85-90 186 111.0 86.3 43.0 32 64 '4 2. 72 80-90 196 98.0 87. 340. 7 23 75 2 2. 64 60-70 190 101. 3 78. 3 41. 3 8 90 2 2. 62 85 200100. 3 95. 7 37. 3 3 2 30 16 50 2. -70 172 58. 0 50. 0 27. 5 4 91 5 2.68' '90 158 96. 0 96. 3 45. 0 8 7 17 9 2- 6 2 3.75 50 136 54.8 62.4 27.850 48 2 3.00 6070. 184 57.0 48.3 28.0 r 38 6 1 55 2.69 50-60 169 63.658.0 33.4 100' 2.62 80 90 187 93.7 84.3 38.3 55 45 2.93 80-85 188 96.386.7 39.7 2.52 50 168 67.3 53.7 28.0 54.3 43.4 26.0

in examples is an extracted pinewood-type resin, hereinafter referred toas substantially petroleumhydrocarbon insoluble pine wood resinfi Thisresin is that which isisolated from pine wood in the following'mannerzThe pine wood, which may or may not have" beens'tearne'd to removevolatileconstituents, suchasturpentine and; pine oil, is extracted witha coal tar hydrocarbon-such as benzene or toluene, and the ex- ;tractisthen freed of'yolatile constituents, leaving; aresinous residueconsisting of a mixture of wood rosin and therresin in the presentcomposition; The rosin is dissolved and; removed fiomthe residue byextraction with a petroleum hydrocarbon, such as gasoline. .The'resinous residue remaining after the petroleum hydrocarbon extractionislowinabietic acid. This resin,.low in abietic acid,

1.8 th s liwhich comprises f the resin employed accdrdcommas;Wilmington, Delaware.

The fatty acids and mixtures of fatty acids function as a plasticiner or.introfier for the resin. The-fatty acid placticizing agentsenabletheresin to quickly penetrate the surface of the paper and causesubstantially thorough impregnation of the resin throughout thepaper atrelatiYely low. temperatures.- The preferred fatty acids useful fortheplasticization or introf action ofthe substantially petroleumhydrocarbon insoluble pine wood resin for the purposes of this inventionare the saturated andunsaturated fattyIacids having from eight toeighteen carbon atoms. As shown in the table. the fatty "acid content ofthe compositions may vary'from 10 to 70 percent of the total, by weight,with. the balance being the substantially petroleum hydrocarboninsoluble pine wood resin. For the reasons which will appear below, the.preferred composition is that which has a fatty acid content ofapproximately to 50 percent. p

The plasticized substantially petroleum hydrocarbon insoluble pine woodresin is applied to the paper in a molten'. state. Plasticization of ithe resin may be accomplished by heating'a'mixture of the unmelted resinand thefatty acid plact icizing agent. The mixture is stirredsufliciently to obtain a uniform dispersion of the plasticizing agent inthe resin. Themolten plasticized resin is maintained at a temperaturebelow that which will Chat or burnthe paper, preferably about 325 F. to33 5- .F., although temperatures as high as 400 F. to 415 F. have beenused. Afterthe plasticized resin is applied to the surface of the paperin the form-"of a coating, the coated paper is heat treatedto cause theplasticized resin to become impregnated in the paper. Again, in thepractice of this invention, the temperature of the heat-treating stepneed, not be in excess of that temperature which will heat-damage thepaper, but, of course, should be above the flow-point. temperature oftheplasticized resin. In the examples cited in the table, a method using aminimum of operational steps was used. In the'method used, the paper ispassed between two hot rolls. The lower roll is in contact with, orpartially submerged in, a molten bath of the plasticized resin. Thelower roll serves to'pick up the molten plasticiz'ed resin and coat theside of the paper which is passed in contact with the lower roll.The'upper roll may be used to cause partial impregnation 0f theplasticized resin as it is coated on thepaper by pressing the paper uponthe lower pick-up roll. The paper maythen be continuously brought intocontactwith another heated roll. This subseqeunt contact with the heatedroll constitutes the heat-treating step which causes the impregnation ofthe plasticized resin into the paper. The impregnated paper does nothave a glossy coating over the surface. The surface of the paperadvantageously retains its compatibility with combining or laminatingadhesives.

This example describes an application method for coating andimpregnating one side of the web under treat? ment. It will beunderstood that provision for application of the molten, plasticized;resinous impregnating eomposition to either one side or both sides ofthe web receiving impregnation shall be within the scope of this ve i n.i

In the table, Examples 1 through 13 show a variety of mixtures ofpalmitic, stearic, and olcic acids as' plasticizing agents combined invarious proportions with the substantially pe troleum hydrocarboninsoluble resin. Examples 14 through 16;are directed to'plasticizingagents containing lower fatty acids, thelowest fatty acid having aminimum of eight carbon atoms. Examples 17 and 18 are directed toplasticizing agents containing the higher fatty acids, the'highest fattyacid having a maximum of eighteen carbon atoms. The plasticizing agentsof Examplesi'17 and 18 also containan amount of miscellane to eighteencarbon atoms. The fatty acids of Example 17 are commonly known as talloil fatty acids. The fatty acids of Example 18 are those derived fromdistilled palm oil and are commercially available under the trade nameEmery 640, marketed by Emery Industries, Inc. The plasticizing agent ofExample 19 is rubber grade stearic acid and is available from a numberof commercial sources, such as General Mills, Inc. Example 20 shows aplasticizing agent consisting of palmitic and stearic acids in aboutequal proportions. Example 21 is illustrative of a plasticizing agentconsisting of a mixture offatty acids present in tallow, commonly knownas tallow fatty acids. Example 22 is an untreated sample of thecorrugating material. Its wilt-resistant characteristics are given forpurposes of comparison with the same paper treated in accordance withthe present invention.

Reference to the test-data columns'shows the rapidity at which theplasticized resin composition penetrates and impregnates the paper. Thetime of penetration is determined by pressing a 4-inch by 6-inch pieceof paper as it comes from the pick-up roll against a stationary rollwhich is maintained at a temperature of 330 'F. This temperature is wellwithin the range of temperatures which will not char 'or otherwiseheat-damage the paper. The degree or percent of penetration of theplasticized resin into the paper is determined by measuring the extentto which the impregnating material soaks or migrates into a sheet ofpaper. For example, a 10-point sheet (.010- inch thick) which isimpregnated in accordance with the present'inventionto a depth of 8points (.008'inch) has an 80 percent penetration of the plasticizedresin.

In addition to functioning as a plasticizing agent for the substantiallypetroleum hydrocarbon insoluble pine wood resin, the fatty acids affecta lowering of the flowpoint temperature of the resin. In comparison withthe values of the table, the flow point temperature of the unplasticizedresin is 240 F. A fatty acid content of 30 to 50 percent provides anadequate lowering of the melt temperature to give a satisfactory degreeof impregnation for wiltproofing the paper.

The temperature at which the plasticized resin will begin to flow isdetermined by a modified Columbia method. In this method a 1-inch testtube is supported in the center of a beaker filled with mineral oil. Athermometer bulb is two-thirds coated by dipping into the moltenplasticized resin, and removing at a slow, even rate. When cool, thethermometer is then suspended in the center of the test tube. Themineral oil is then heated, and the temperature at which a drop of theplasticized resin falls from the thermometer bulb is recorded as theflow point. v

The wilt-resistant and crush-strength properties of the plain andimpregnated corrugating material paper 'were determined by the ConcoraMedium Test. Essentially, this test consists of cutting an accurate6-inch by /2'- inch specimen and then corrugating the specimen through afluter. The corrugated sample is placed on a rack with flutes matchingthe configuration of the sample. A comb is placed over the sample tohold it in place and a strip of A-inch wide tape is adhered to it. Thenthe comb is removed and the resulting sample strip of socalled singleface is placed between the platens of" a fiat crush tester. The force inpounds necessary to crush the sample is the test result. This testingprocedure is more particularly described in the article -entitled A newtest for corrugating medium, by F. D. Long and G. G. Maltenfort,published in Fiber Containers and Paperboard Mills, pp. 86 to 92(December 1952). Specimens of each of the examples were subjected toflat crush testing immediately after Concora fiuting and single facesample fabrication. Other specimens of each of the examples were testedafter 1 days exposure to 5 0 percent relative hum'idityto bring "the-specimens to a stateiof moisture equilibrium therewith. In addition,specimens of each of these examples were tested after :three' daysexposure to the extreme condition of percent relative humidity. Thevalues for these tests are set forth in the last three columns of thetable. The Concora 'Medium Test results for untreated corrugatingmaterial paper. are recorded as Example 22. Comparison of these valuesfor Examples 1 through 21 with the values for the untreated corrugatingmaterial paper of Example 22 shows the improved wilt-resistantproperties of the paper treated with the fatty acid plasticized resin ofthe present invention.

Examples given in this specification are illustrative of the plasticizedresinous impregnating composition dis closed herein, but are not to beconstrued as limiting said impregnation composition.

It will be understood that impregnation or treatment of paper componentssubsequently to be combined or laminated into corrugated fibreboardand/or solid fibreboard and utilized as such shall be within the scopeof this invention. Conventional use of the impregnated paper componentin corrugated fibreboard shall be as the inner component of thefibrebo'ard known as corrugated material, but the other components canreceive like treat merit also. The commercial material known as solidfibreboard differs from corrugated fibreboard in that all plies of thesolid fibreboard are in intimate continuous contact one with the other.Any one or all of the component paperboard plies of fibreboard can be impregnated by methods disclosed herein prior to final com bination as thesaid solid fibreboard.

In summary, it is seen that the fatty acid plasticizing agent enablesthe resin to easily and quickly penetrate into the paper. The process ofimpregnating the paper involves a minimum of procedural steps and,therefore, has the advantage of being adapted to use with existingcommercial equipment. The fatty acid plasticized substantially petroleumhydrocarbon insoluble pine wood resin imparts increased wilt-resistantproperties to the paper as evidenced by the increased strength andrigidity of the treated paper under conditions of ex'posure.t0 normaland relatively high humidity.

What is claimed is:

1. The method of imparting wilt-resistant properties to paper comprisingcoating the paper with molten plasticized resin, said plasticized resincomprising from about 30 to percent of substantially petroleumhydrocarbon insoluble pine wood resin and the balance at least one fattyacid as a plasticizer, and thereafter contacting the coated paperagainst a heated surface to impregnate the paper with said resin.

2. The method of imparting wilt-resistant properties to paper comprisingcoating the paper with molten plasticized resin, said plasticized resincomprising from about 30 to 90 percent of substantially petroleumhydrocarbon insoluble pine wood resin and the balance at least one fattyacid having from 8 to 18 carbon atoms as a plasticizer, and thereaftercontacting the coated paper against a heated surface to impregnate thepaper with said resin.

3. The method of imparting wilt-resistant properties to paper comprisingcoating'the paper with molten plasticized resin, saidplasticized resincomprising from about 30 to 90 percent of substantially petroleumhydrocarbon insoluble pine wood resin and the balance stearic acid as aplasticizer, and thereafter contacting the coated paper against a heatedsurface to impregnate the paper with said resin.

4. The method of imparting wilt-resistant properties to paper comprisingcoating the paper with molten plasticized resin, said plasticized resincomprising from about 30 to 90 percent of substantially petroleumhydrocarbon insoluble pine wood resin and the balance a mixture oflauric, myristic, and palmitic acids as a plasticizer, and

30 to 90 percent of substantially petroleum hydrocarbon insoluble'pinewood resin and the balance tallow fatty acids as a plasticizer, andthereafter contacting the coated paper against a heated surface toimpregnate'the paper withsaid'resin. A t a 6. Ina methodfofmakingcor'rugating material for corrugated fibreboard construction, thestep of imparting wilt-resistant properties to said corrugating materialcomprising impregnating paper with molten plasticized resin, saidplasticized resincomp'rising from "about 30 to 90'percent ofsubstantially petroleum hydrocarbon insoluble pine wood resin and thebalance at least one fattyacid as a plasticizer, and corrugating theimpregnated P e -.4 J I 7.-In a. method of making corrugating materialfor corrugated fibreboard construction, "the step of impartingwilt-resistant propertiesfto said corrugating material comprisingimpregnating paper with molten plasticized resin, said plasticizedresincomprising from about 30 to paper, said plasticized' resincomprising from about 30.

to 90 percent of substantially petroleum hydrocarbon insoluble pine wood resin and the balance at least one fatty acid having fron i 8 to 18carbon atoms as a plasticizer. 10. A corrugating material havingimproved wilt-resist ant properties comprising plasticizedresin-impregnated paper, said plasticized resin comprising from about 30to 90 percent of substantially petroleum hydrocarbon insoluble pine woodresin and the balance stearic acid as a plasticizer. t

11;? Acorrugatingmaterial having improved wilt-resistant propertiesoomprising plasticized resin-impregnated paper, said plasticized resincomprising from about 30 to 90 percent of substantially petroleumhydrocarbon insoluble pine wood resin and. the. balance a mixture oflauric acid, myristic acid, and palmitic acid asa plasticizer. r

12. A corrugating material having improved wilt-resistant propcrtiescomprising plasticized resin-impregnated paper, said plasticized resincomprising from about 30 to90 percent of substantially petroleumhydrocarbon insoluble pine wood resin and the balance tallow fatty acidsas a plasticizer.

l3. A'papcrboard sheet suitable for use as at least one of the facingcomponents of corrugated fibreboard, said sheet comprising plasticizedresinimpregnated paperboard, said plasticized resin comprising fromabout 30 to 90 percent of substantially petroleum hydrocarbon insolublepine' wood resin and the balance at least one fatty acid as aplasticizer. V t

1 14. A paperboard sheet suitable for use as at least one of 'thefacing.components of corrugated fibreboard, said sheet having increasedwilt-resistant properties comprising plasticized resindmpregnatedpaperboard, said plasticized resin comprising from about 30 to 90percent of substantially petroleum hydrocarbon insoluble pine wood resinand the balance at least one fatty acid having from 8 to 18 carbonatomsasa plasticizer. I 15. Paper suitable'for inclusion as at least oneof the components-of fibreboard, said paper comprising plasticizedresin-impregnated paper, said plasticized 'r esin comprising from aboutto 90 percent of substantially petroleum hydrocarbon insoluble pine woodresin and the balance at least one fatty acid as a plasticizer.

16. Paper suitablefor use as at least one of the components offibreboard, said paper having increased wiltresistant propertiescomprising plasticized resin-impregnated paper, said plasticizedv resincomprising from about 3010 90 percent of substantially petroleumhydrocarbon insolublepine wood resin and the balance at least one fattyacid having'from 8 to 18 carbon atoms as a plasticizer. r a

17. A hot-melt ,resinous composition for wilt-proofing paper orpaperboard comprising from about 30 to 90 percent of substantiallypetroleum hydrocarbon insoluble pine wood resin and the balance at leastone fatty acid as a plasticizer, said composition characterized by alowmelt viscosity below that of said pine wood resin without saidplasticizer-and the ability to rapidly penetrate and impregnate thepaper. I

18. A hot-melt resinous composition for wilt-proofing paper orpaperboard comprising from about 30 to 90 percent of substantiallypetroleum hydrocarbon insoluble pine wood resin and the balance at leastone fatty acid having from 8 to 18 carbon atoms as a plasticizer, saidcomposition characterized by a low-melt viscosity below that of the saidpine wood resin without said plasticizer and the' ability to rapidlypenetrate andimpregnate the paper. a

19. A hot-melt resinous composition for wilt-proofing paper orpaperboard comprising from about 30 to 90 percent of substantiallypetroleum hydrocarbon insoluble pine wood resinand the balance stearicacid as a plasticizer, said composition characterized by a low-meltviscosity below that of the said pine wood resin without saidplasticizer and the ability 'to rapidly penetrate and impregnate thepaper.

.20. A hot-melt resinous composition for wilt-proofing paper orpaperboard comprising from about 30 to percent of substantiallypetroleum hydrocarbon insoluble pine wood resin and the balance amixture of laun'c, myristic, and palmitic acids as a plasticizer, saidcomposition characterized by a low-melt viscosity below that of thesaid'pine wood resin without said plasticizer and the ability to rapidlypenetrate and impregnate the paper. 21. A hot-melt resinous compositionfor wilt-proofing paper or paperboard comprising from about 30 to 90percent of substantially petroleum hydrocarbon insoluble pine wood resinand the balance tallow fatty acids as a plasticizer, said resincomposition characterized by a low-melt viscosity below that of the saidpine wood resin without said plasticizer and the ability to rapidlypenetrate and impregnate paper.

, References Cited in the file of this patent UNITED STATES PATENTSUNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,840,138 June 24, 1958 Herbert NA Johnston et a1,

It is herebfii certified that error appears in the-printed specificationof the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column 5 line '75, for ''after 1 day's exposure to 50 percent" readafter exposure to 50 percent n Signed and sealed this 9th day ofSeptember 1958,

( SEAL) Attest:

KARL H-o AIEINE v ROBERT C. WATSON \ttesting Officer Commissioner ofPatents

7. IN A METHOD OF MAKING CORRUGATING MATERIAL FOR CORRUGATED FIBREBOARDCONSTRUCTION, THE STEP OF IMPARTING WILT-RESISTANT PROPERTIES TO SAIDCORRUGATING MATERIAL COMPRISING IMPREGNATING PAPER WITH MOLTENPLASTICIZED RESIN, SAID PLASTICIZED RESIN COMPRISING FROM ABOUT 30 TO 90PERCENT OF SUBSTANTIALLY PETROLEUM HYDROCARBON INSOLUBLE PINE WOOD RESINAND THE BALANCE AT LEAST ONE FATTY ACID HAVING FROM 8 TO 18 CARBON ATOMSAS A PLASTICIZER, AND CORRUGATING THE IMPREGNATED PAPER.